Fifty-eight percent of pool filter samples taken from Atlanta area pools last summer contained E. coli, a bacteria found in human feces.

The report is a sign that swimmers often contaminate pool water when they have a “fecal incident” in the water, or when human waste washes off their bodies because they don’t shower thoroughly before hitting the water, according to the report from the U.S. Centers for Disease Control and Prevention.

And while the study only focused on pools in the Atlanta region, the researchers said it’s likely that fecal contamination from swimmers is a problem in public pools throughout the country. The study did not look at water parks, residential pools or other types of recreational water.

... “chlorine and other disinfectants don’t kill germs instantly. That’s why it’s important for swimmers to protect themselves by not swallowing the water they swim in and to protect others by keeping feces and germs out of the pool by taking a pre-swim shower and not swimming when ill with diarrhea. [emphasis mine]